The present invention relates to a device for adaptive distance and speed control in motor vehicles as it is described, for instance, in SAE paper no. 96 10 10 “Adaptive Cruise Control, System Aspects and Development Trends”, Winner et al., 1996. Such a device, which is also referred to as ACC system (Adaptive Cruise Control), allows the speed of the vehicle to be automatically controlled to a driver-selected target speed. Furthermore, objects located in front of the vehicle are detected by a sensor device, for instance with the aid of a radar sensor. When the sensor device detects a target object, typically a vehicle traveling immediately ahead in the own traffic lane, the speed of the own vehicle is reduced, if necessary by intervening in actuating elements of the drive and/or brake system, in such a way that the target object is tracked within a certain safety distance. This distance is a function of the speed and determined by a time gap, which is driver-selectable within certain limits and which indicates the time interval at which the own vehicle is following the vehicle driving ahead.
Utilizing the radar sensor, it is possible to directly measure not only the distance, but also the relative speed of the preceding vehicle. As an option, the relative speed may also be determined by time derivation of the measured distance. When the absolute speed of the vehicle driving ahead, i.e., the sum of the speed V of the regulated vehicle and the measured relative speed Vr, increases beyond the driver-desired speed Vset, setpoint speed Vsetpoint—calculated within the framework of distance control—of the regulated vehicle is restricted to desired speed Vset. When the regulated vehicle is traveling at desired speed Vset and approaching a vehicle driving ahead at a slower speed, the distance control function ensures that the speed V of the regulated vehicle will be gradually reduced when falling below a certain distance that is a function of the relative speed, taking the driving comfort into account, so that the speed is adapted to the speed of the preceding vehicle while the distance to the preceding vehicle is reduced to the value determined by the time gap.
To increase the driving comfort, the conventional ACC systems include a so-called torque dampener, which restricts the actuating variables that are output to the actuating elements and/or their change as a function of time. For instance, the torque dampener has the function of limiting the positive or negative setpoint accelerations, represented by the actuating variables, as well as their time derivatives, so that abrupt transitions are avoided, thereby achieving a smooth operation that is perceived as comfortable.
In addition, vehicle guidance systems have been proposed, which, possibly in combination with an ACC system, have a so-called crash mitigation function, which automatically initiates full braking when a crash with another vehicle seems imminent, naturally without torque dampening, so that the collision may still be prevented or the results of the collision at least be reduced.